Epilepsy is one of the oldest brain disorders known to mankind and a common neurological condition that affects individuals of all ages. Temporal lobe epilepsy (TLE) is the most common form of acquired epilepsy and usually develops after a precipitating injury to the brain. The process that transforms a normal brain into an epileptic one is known as epileptogenesis and includes a series of molecular, biochemical and structural changes. During epileptogenesis there is a transient decline in GABAergic drive and increased excitability that can be detected as abnormal electroencephalographic signals. The origin of this hyperexcitability is unclear but it has been proposed that a loss of inhibitory drive might contribute to a loss of the excitation/inhibition balance. Our overall hypothesis is that calpain-mediated proteolysis of GABAergic synapses during the latent period is key to the pathogenesis of epilepsy and its prevention. Our preliminary data indicate that (i) during the latent period, there is a loss of GABAergic proteins that is paralleled by calpain overactivation; and (ii) pharmacological inhibition of calpain reduces seizure burden. To test this idea, we propose the following aims: Aim I. Examine the Integrity of Inhibitory Synapses during epileptogenesis. We hypothesize that cleavage of GABAergic proteins by calpain promotes hyperexcitability. To test this hypothesis, we will use in vitro (cultured neurons) and in vivo (rodent models of TLE) experiments to characterize (i) the cleavage of ?-spectrin, a marker of calpain activation; (ii) te cleavage of scaffolding proteins and receptors necessary for proper inhibitory neurotransmission; (iii) the synaptic distribution of scaffolding proteins and GABA receptors; (iv) the plasma membrane distribution of GABAAR receptors; and, (v) the effects of calpain overactivation on the electrophysiological properties of inhibitory synapses. Aim II. Evaluate the Role of Calpain-Dependent Proteolysis in Epileptogenesis. We hypothesize that inhibition of calpain during the latent period might prevent epileptogenesis and its associated pathologies. To test this hypothesis, we will use two models of TLE (pilocarpine and intrahippocampal kainate) to evaluate the effect of pharmacological and genetic inhibition of calpain on (i) seizure burden; (ii) the cellular/molecular alterations that occur during the latent period; and (iii) cognitive dysfunction associated with epilepsy. When concluded, our studies will delineate the role of calpain-mediated proteolysis in the pathogenesis of epilepsy and will provide a proof of principle for the use of calpain inhibitors as a novel approach to prevent epilepsy.